1 /*
2  * storage_common.c -- Common definitions for mass storage functionality
3  *
4  * Copyright (C) 2003-2008 Alan Stern
5  * Copyeight (C) 2009 Samsung Electronics
6  * Author: Michal Nazarewicz (m.nazarewicz@samsung.com)
7  *
8  * Ported to u-boot:
9  * Andrzej Pietrasiewicz <andrzej.p@samsung.com>
10  *
11  * Code refactoring & cleanup:
12  * Łukasz Majewski <l.majewski@samsung.com>
13  *
14  * SPDX-License-Identifier:	GPL-2.0+
15  */
16 
17 
18 /*
19  * This file requires the following identifiers used in USB strings to
20  * be defined (each of type pointer to char):
21  *  - fsg_string_manufacturer -- name of the manufacturer
22  *  - fsg_string_product      -- name of the product
23  *  - fsg_string_serial       -- product's serial
24  *  - fsg_string_config       -- name of the configuration
25  *  - fsg_string_interface    -- name of the interface
26  * The first four are only needed when FSG_DESCRIPTORS_DEVICE_STRINGS
27  * macro is defined prior to including this file.
28  */
29 
30 /*
31  * When FSG_NO_INTR_EP is defined fsg_fs_intr_in_desc and
32  * fsg_hs_intr_in_desc objects as well as
33  * FSG_FS_FUNCTION_PRE_EP_ENTRIES and FSG_HS_FUNCTION_PRE_EP_ENTRIES
34  * macros are not defined.
35  *
36  * When FSG_NO_DEVICE_STRINGS is defined FSG_STRING_MANUFACTURER,
37  * FSG_STRING_PRODUCT, FSG_STRING_SERIAL and FSG_STRING_CONFIG are not
38  * defined (as well as corresponding entries in string tables are
39  * missing) and FSG_STRING_INTERFACE has value of zero.
40  *
41  * When FSG_NO_OTG is defined fsg_otg_desc won't be defined.
42  */
43 
44 /*
45  * When FSG_BUFFHD_STATIC_BUFFER is defined when this file is included
46  * the fsg_buffhd structure's buf field will be an array of FSG_BUFLEN
47  * characters rather then a pointer to void.
48  */
49 
50 
51 /* #include <asm/unaligned.h> */
52 
53 
54 /*
55  * Thanks to NetChip Technologies for donating this product ID.
56  *
57  * DO NOT REUSE THESE IDs with any other driver!!  Ever!!
58  * Instead:  allocate your own, using normal USB-IF procedures.
59  */
60 #define FSG_VENDOR_ID	0x0525	/* NetChip */
61 #define FSG_PRODUCT_ID	0xa4a5	/* Linux-USB File-backed Storage Gadget */
62 
63 /*-------------------------------------------------------------------------*/
64 
65 #ifndef DEBUG
66 #undef VERBOSE_DEBUG
67 #undef DUMP_MSGS
68 #endif /* !DEBUG */
69 
70 #ifdef VERBOSE_DEBUG
71 #define VLDBG	LDBG
72 #else
73 #define VLDBG(lun, fmt, args...) do { } while (0)
74 #endif /* VERBOSE_DEBUG */
75 
76 /*
77 #define LDBG(lun, fmt, args...)   dev_dbg (&(lun)->dev, fmt, ## args)
78 #define LERROR(lun, fmt, args...) dev_err (&(lun)->dev, fmt, ## args)
79 #define LWARN(lun, fmt, args...)  dev_warn(&(lun)->dev, fmt, ## args)
80 #define LINFO(lun, fmt, args...)  dev_info(&(lun)->dev, fmt, ## args)
81 */
82 
83 #define LDBG(lun, fmt, args...) do { } while (0)
84 #define LERROR(lun, fmt, args...) do { } while (0)
85 #define LWARN(lun, fmt, args...) do { } while (0)
86 #define LINFO(lun, fmt, args...) do { } while (0)
87 
88 /*
89  * Keep those macros in sync with those in
90  * include/linux/usb/composite.h or else GCC will complain.  If they
91  * are identical (the same names of arguments, white spaces in the
92  * same places) GCC will allow redefinition otherwise (even if some
93  * white space is removed or added) warning will be issued.
94  *
95  * Those macros are needed here because File Storage Gadget does not
96  * include the composite.h header.  For composite gadgets those macros
97  * are redundant since composite.h is included any way.
98  *
99  * One could check whether those macros are already defined (which
100  * would indicate composite.h had been included) or not (which would
101  * indicate we were in FSG) but this is not done because a warning is
102  * desired if definitions here differ from the ones in composite.h.
103  *
104  * We want the definitions to match and be the same in File Storage
105  * Gadget as well as Mass Storage Function (and so composite gadgets
106  * using MSF).  If someone changes them in composite.h it will produce
107  * a warning in this file when building MSF.
108  */
109 
110 #define DBG(d, fmt, args...)     debug(fmt , ## args)
111 #define VDBG(d, fmt, args...)    debug(fmt , ## args)
112 /* #define ERROR(d, fmt, args...)   printf(fmt , ## args) */
113 /* #define WARNING(d, fmt, args...) printf(fmt , ## args) */
114 /* #define INFO(d, fmt, args...)    printf(fmt , ## args) */
115 
116 /* #define DBG(d, fmt, args...)     do { } while (0) */
117 /* #define VDBG(d, fmt, args...)    do { } while (0) */
118 #define ERROR(d, fmt, args...)   do { } while (0)
119 #define WARNING(d, fmt, args...) do { } while (0)
120 #define INFO(d, fmt, args...)    do { } while (0)
121 
122 #ifdef DUMP_MSGS
123 
124 /* dump_msg(fsg, const char * label, const u8 * buf, unsigned length); */
125 # define dump_msg(fsg, label, buf, length) do {                         \
126 	if (length < 512) {						\
127 		DBG(fsg, "%s, length %u:\n", label, length);		\
128 		print_hex_dump(KERN_DEBUG, "", DUMP_PREFIX_OFFSET,	\
129 			       16, 1, buf, length, 0);			\
130 	}								\
131 } while (0)
132 
133 #  define dump_cdb(fsg) do { } while (0)
134 
135 #else
136 
137 #  define dump_msg(fsg, /* const char * */ label, \
138 		   /* const u8 * */ buf, /* unsigned */ length) do { } while (0)
139 
140 #  ifdef VERBOSE_DEBUG
141 
142 #    define dump_cdb(fsg)						\
143 	print_hex_dump(KERN_DEBUG, "SCSI CDB: ", DUMP_PREFIX_NONE,	\
144 		       16, 1, (fsg)->cmnd, (fsg)->cmnd_size, 0)		\
145 
146 #  else
147 
148 #    define dump_cdb(fsg) do { } while (0)
149 
150 #  endif /* VERBOSE_DEBUG */
151 
152 #endif /* DUMP_MSGS */
153 
154 /*-------------------------------------------------------------------------*/
155 
156 /* SCSI device types */
157 #define TYPE_DISK	0x00
158 #define TYPE_CDROM	0x05
159 
160 /* USB protocol value = the transport method */
161 #define USB_PR_CBI	0x00		/* Control/Bulk/Interrupt */
162 #define USB_PR_CB	0x01		/* Control/Bulk w/o interrupt */
163 #define USB_PR_BULK	0x50		/* Bulk-only */
164 
165 /* USB subclass value = the protocol encapsulation */
166 #define USB_SC_RBC	0x01		/* Reduced Block Commands (flash) */
167 #define USB_SC_8020	0x02		/* SFF-8020i, MMC-2, ATAPI (CD-ROM) */
168 #define USB_SC_QIC	0x03		/* QIC-157 (tape) */
169 #define USB_SC_UFI	0x04		/* UFI (floppy) */
170 #define USB_SC_8070	0x05		/* SFF-8070i (removable) */
171 #define USB_SC_SCSI	0x06		/* Transparent SCSI */
172 
173 /* Bulk-only data structures */
174 
175 /* Command Block Wrapper */
176 struct fsg_bulk_cb_wrap {
177 	__le32	Signature;		/* Contains 'USBC' */
178 	u32	Tag;			/* Unique per command id */
179 	__le32	DataTransferLength;	/* Size of the data */
180 	u8	Flags;			/* Direction in bit 7 */
181 	u8	Lun;			/* LUN (normally 0) */
182 	u8	Length;			/* Of the CDB, <= MAX_COMMAND_SIZE */
183 	u8	CDB[16];		/* Command Data Block */
184 };
185 
186 #define USB_BULK_CB_WRAP_LEN	31
187 #define USB_BULK_CB_SIG		0x43425355	/* Spells out USBC */
188 #define USB_BULK_IN_FLAG	0x80
189 
190 /* Command Status Wrapper */
191 struct bulk_cs_wrap {
192 	__le32	Signature;		/* Should = 'USBS' */
193 	u32	Tag;			/* Same as original command */
194 	__le32	Residue;		/* Amount not transferred */
195 	u8	Status;			/* See below */
196 };
197 
198 #define USB_BULK_CS_WRAP_LEN	13
199 #define USB_BULK_CS_SIG		0x53425355	/* Spells out 'USBS' */
200 #define USB_STATUS_PASS		0
201 #define USB_STATUS_FAIL		1
202 #define USB_STATUS_PHASE_ERROR	2
203 
204 /* Bulk-only class specific requests */
205 #define USB_BULK_RESET_REQUEST		0xff
206 #define USB_BULK_GET_MAX_LUN_REQUEST	0xfe
207 
208 /* CBI Interrupt data structure */
209 struct interrupt_data {
210 	u8	bType;
211 	u8	bValue;
212 };
213 
214 #define CBI_INTERRUPT_DATA_LEN		2
215 
216 /* CBI Accept Device-Specific Command request */
217 #define USB_CBI_ADSC_REQUEST		0x00
218 
219 /* Length of a SCSI Command Data Block */
220 #define MAX_COMMAND_SIZE	16
221 
222 /* SCSI commands that we recognize */
223 #define SC_FORMAT_UNIT			0x04
224 #define SC_INQUIRY			0x12
225 #define SC_MODE_SELECT_6		0x15
226 #define SC_MODE_SELECT_10		0x55
227 #define SC_MODE_SENSE_6			0x1a
228 #define SC_MODE_SENSE_10		0x5a
229 #define SC_PREVENT_ALLOW_MEDIUM_REMOVAL	0x1e
230 #define SC_READ_6			0x08
231 #define SC_READ_10			0x28
232 #define SC_READ_12			0xa8
233 #define SC_READ_CAPACITY		0x25
234 #define SC_READ_FORMAT_CAPACITIES	0x23
235 #define SC_READ_HEADER			0x44
236 #define SC_READ_TOC			0x43
237 #define SC_RELEASE			0x17
238 #define SC_REQUEST_SENSE		0x03
239 #define SC_RESERVE			0x16
240 #define SC_SEND_DIAGNOSTIC		0x1d
241 #define SC_START_STOP_UNIT		0x1b
242 #define SC_SYNCHRONIZE_CACHE		0x35
243 #define SC_TEST_UNIT_READY		0x00
244 #define SC_VERIFY			0x2f
245 #define SC_WRITE_6			0x0a
246 #define SC_WRITE_10			0x2a
247 #define SC_WRITE_12			0xaa
248 
249 /* SCSI Sense Key/Additional Sense Code/ASC Qualifier values */
250 #define SS_NO_SENSE				0
251 #define SS_COMMUNICATION_FAILURE		0x040800
252 #define SS_INVALID_COMMAND			0x052000
253 #define SS_INVALID_FIELD_IN_CDB			0x052400
254 #define SS_LOGICAL_BLOCK_ADDRESS_OUT_OF_RANGE	0x052100
255 #define SS_LOGICAL_UNIT_NOT_SUPPORTED		0x052500
256 #define SS_MEDIUM_NOT_PRESENT			0x023a00
257 #define SS_MEDIUM_REMOVAL_PREVENTED		0x055302
258 #define SS_NOT_READY_TO_READY_TRANSITION	0x062800
259 #define SS_RESET_OCCURRED			0x062900
260 #define SS_SAVING_PARAMETERS_NOT_SUPPORTED	0x053900
261 #define SS_UNRECOVERED_READ_ERROR		0x031100
262 #define SS_WRITE_ERROR				0x030c02
263 #define SS_WRITE_PROTECTED			0x072700
264 
265 #define SK(x)		((u8) ((x) >> 16))	/* Sense Key byte, etc. */
266 #define ASC(x)		((u8) ((x) >> 8))
267 #define ASCQ(x)		((u8) (x))
268 
269 struct device_attribute { int i; };
270 #define ETOOSMALL	525
271 
272 #include <usb_mass_storage.h>
273 
274 /*-------------------------------------------------------------------------*/
275 
276 struct fsg_lun {
277 	loff_t		file_length;
278 	loff_t		num_sectors;
279 
280 	unsigned int	initially_ro:1;
281 	unsigned int	ro:1;
282 	unsigned int	removable:1;
283 	unsigned int	cdrom:1;
284 	unsigned int	prevent_medium_removal:1;
285 	unsigned int	registered:1;
286 	unsigned int	info_valid:1;
287 	unsigned int	nofua:1;
288 
289 	u32		sense_data;
290 	u32		sense_data_info;
291 	u32		unit_attention_data;
292 
293 	struct device	dev;
294 };
295 
296 #define fsg_lun_is_open(curlun)	((curlun)->filp != NULL)
297 #if 0
298 static struct fsg_lun *fsg_lun_from_dev(struct device *dev)
299 {
300 	return container_of(dev, struct fsg_lun, dev);
301 }
302 #endif
303 
304 /* Big enough to hold our biggest descriptor */
305 #define EP0_BUFSIZE	256
306 #define DELAYED_STATUS	(EP0_BUFSIZE + 999)	/* An impossibly large value */
307 
308 /* Number of buffers we will use.  2 is enough for double-buffering */
309 #define FSG_NUM_BUFFERS	2
310 
311 /* Default size of buffer length. */
312 #define FSG_BUFLEN	((u32)16384)
313 
314 /* Maximal number of LUNs supported in mass storage function */
315 #define FSG_MAX_LUNS	8
316 
317 enum fsg_buffer_state {
318 	BUF_STATE_EMPTY = 0,
319 	BUF_STATE_FULL,
320 	BUF_STATE_BUSY
321 };
322 
323 struct fsg_buffhd {
324 #ifdef FSG_BUFFHD_STATIC_BUFFER
325 	char				buf[FSG_BUFLEN];
326 #else
327 	void				*buf;
328 #endif
329 	enum fsg_buffer_state		state;
330 	struct fsg_buffhd		*next;
331 
332 	/*
333 	 * The NetChip 2280 is faster, and handles some protocol faults
334 	 * better, if we don't submit any short bulk-out read requests.
335 	 * So we will record the intended request length here.
336 	 */
337 	unsigned int			bulk_out_intended_length;
338 
339 	struct usb_request		*inreq;
340 	int				inreq_busy;
341 	struct usb_request		*outreq;
342 	int				outreq_busy;
343 };
344 
345 enum fsg_state {
346 	/* This one isn't used anywhere */
347 	FSG_STATE_COMMAND_PHASE = -10,
348 	FSG_STATE_DATA_PHASE,
349 	FSG_STATE_STATUS_PHASE,
350 
351 	FSG_STATE_IDLE = 0,
352 	FSG_STATE_ABORT_BULK_OUT,
353 	FSG_STATE_RESET,
354 	FSG_STATE_INTERFACE_CHANGE,
355 	FSG_STATE_CONFIG_CHANGE,
356 	FSG_STATE_DISCONNECT,
357 	FSG_STATE_EXIT,
358 	FSG_STATE_TERMINATED
359 };
360 
361 enum data_direction {
362 	DATA_DIR_UNKNOWN = 0,
363 	DATA_DIR_FROM_HOST,
364 	DATA_DIR_TO_HOST,
365 	DATA_DIR_NONE
366 };
367 
368 /*-------------------------------------------------------------------------*/
369 
370 static inline u32 get_unaligned_be24(u8 *buf)
371 {
372 	return 0xffffff & (u32) get_unaligned_be32(buf - 1);
373 }
374 
375 /*-------------------------------------------------------------------------*/
376 
377 enum {
378 #ifndef FSG_NO_DEVICE_STRINGS
379 	FSG_STRING_MANUFACTURER	= 1,
380 	FSG_STRING_PRODUCT,
381 	FSG_STRING_SERIAL,
382 	FSG_STRING_CONFIG,
383 #endif
384 	FSG_STRING_INTERFACE
385 };
386 
387 #ifndef FSG_NO_OTG
388 static struct usb_otg_descriptor
389 fsg_otg_desc = {
390 	.bLength =		sizeof fsg_otg_desc,
391 	.bDescriptorType =	USB_DT_OTG,
392 
393 	.bmAttributes =		USB_OTG_SRP,
394 };
395 #endif
396 
397 /* There is only one interface. */
398 
399 static struct usb_interface_descriptor
400 fsg_intf_desc = {
401 	.bLength =		sizeof fsg_intf_desc,
402 	.bDescriptorType =	USB_DT_INTERFACE,
403 
404 	.bNumEndpoints =	2,		/* Adjusted during fsg_bind() */
405 	.bInterfaceClass =	USB_CLASS_MASS_STORAGE,
406 	.bInterfaceSubClass =	USB_SC_SCSI,	/* Adjusted during fsg_bind() */
407 	.bInterfaceProtocol =	USB_PR_BULK,	/* Adjusted during fsg_bind() */
408 	.iInterface =		FSG_STRING_INTERFACE,
409 };
410 
411 /*
412  * Three full-speed endpoint descriptors: bulk-in, bulk-out, and
413  * interrupt-in.
414  */
415 
416 static struct usb_endpoint_descriptor
417 fsg_fs_bulk_in_desc = {
418 	.bLength =		USB_DT_ENDPOINT_SIZE,
419 	.bDescriptorType =	USB_DT_ENDPOINT,
420 
421 	.bEndpointAddress =	USB_DIR_IN,
422 	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
423 	/* wMaxPacketSize set by autoconfiguration */
424 };
425 
426 static struct usb_endpoint_descriptor
427 fsg_fs_bulk_out_desc = {
428 	.bLength =		USB_DT_ENDPOINT_SIZE,
429 	.bDescriptorType =	USB_DT_ENDPOINT,
430 
431 	.bEndpointAddress =	USB_DIR_OUT,
432 	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
433 	/* wMaxPacketSize set by autoconfiguration */
434 };
435 
436 #ifndef FSG_NO_INTR_EP
437 
438 static struct usb_endpoint_descriptor
439 fsg_fs_intr_in_desc = {
440 	.bLength =		USB_DT_ENDPOINT_SIZE,
441 	.bDescriptorType =	USB_DT_ENDPOINT,
442 
443 	.bEndpointAddress =	USB_DIR_IN,
444 	.bmAttributes =		USB_ENDPOINT_XFER_INT,
445 	.wMaxPacketSize =	cpu_to_le16(2),
446 	.bInterval =		32,	/* frames -> 32 ms */
447 };
448 
449 #ifndef FSG_NO_OTG
450 #  define FSG_FS_FUNCTION_PRE_EP_ENTRIES	2
451 #else
452 #  define FSG_FS_FUNCTION_PRE_EP_ENTRIES	1
453 #endif
454 
455 #endif
456 
457 static struct usb_descriptor_header *fsg_fs_function[] = {
458 #ifndef FSG_NO_OTG
459 	(struct usb_descriptor_header *) &fsg_otg_desc,
460 #endif
461 	(struct usb_descriptor_header *) &fsg_intf_desc,
462 	(struct usb_descriptor_header *) &fsg_fs_bulk_in_desc,
463 	(struct usb_descriptor_header *) &fsg_fs_bulk_out_desc,
464 #ifndef FSG_NO_INTR_EP
465 	(struct usb_descriptor_header *) &fsg_fs_intr_in_desc,
466 #endif
467 	NULL,
468 };
469 
470 /*
471  * USB 2.0 devices need to expose both high speed and full speed
472  * descriptors, unless they only run at full speed.
473  *
474  * That means alternate endpoint descriptors (bigger packets)
475  * and a "device qualifier" ... plus more construction options
476  * for the configuration descriptor.
477  */
478 static struct usb_endpoint_descriptor
479 fsg_hs_bulk_in_desc = {
480 	.bLength =		USB_DT_ENDPOINT_SIZE,
481 	.bDescriptorType =	USB_DT_ENDPOINT,
482 
483 	/* bEndpointAddress copied from fs_bulk_in_desc during fsg_bind() */
484 	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
485 	.wMaxPacketSize =	cpu_to_le16(512),
486 };
487 
488 static struct usb_endpoint_descriptor
489 fsg_hs_bulk_out_desc = {
490 	.bLength =		USB_DT_ENDPOINT_SIZE,
491 	.bDescriptorType =	USB_DT_ENDPOINT,
492 
493 	/* bEndpointAddress copied from fs_bulk_out_desc during fsg_bind() */
494 	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
495 	.wMaxPacketSize =	cpu_to_le16(512),
496 	.bInterval =		1,	/* NAK every 1 uframe */
497 };
498 
499 #ifndef FSG_NO_INTR_EP
500 
501 static struct usb_endpoint_descriptor
502 fsg_hs_intr_in_desc = {
503 	.bLength =		USB_DT_ENDPOINT_SIZE,
504 	.bDescriptorType =	USB_DT_ENDPOINT,
505 
506 	/* bEndpointAddress copied from fs_intr_in_desc during fsg_bind() */
507 	.bmAttributes =		USB_ENDPOINT_XFER_INT,
508 	.wMaxPacketSize =	cpu_to_le16(2),
509 	.bInterval =		9,	/* 2**(9-1) = 256 uframes -> 32 ms */
510 };
511 
512 #ifndef FSG_NO_OTG
513 #  define FSG_HS_FUNCTION_PRE_EP_ENTRIES	2
514 #else
515 #  define FSG_HS_FUNCTION_PRE_EP_ENTRIES	1
516 #endif
517 
518 #endif
519 
520 static struct usb_descriptor_header *fsg_hs_function[] = {
521 #ifndef FSG_NO_OTG
522 	(struct usb_descriptor_header *) &fsg_otg_desc,
523 #endif
524 	(struct usb_descriptor_header *) &fsg_intf_desc,
525 	(struct usb_descriptor_header *) &fsg_hs_bulk_in_desc,
526 	(struct usb_descriptor_header *) &fsg_hs_bulk_out_desc,
527 #ifndef FSG_NO_INTR_EP
528 	(struct usb_descriptor_header *) &fsg_hs_intr_in_desc,
529 #endif
530 	NULL,
531 };
532 
533 /* Maxpacket and other transfer characteristics vary by speed. */
534 static struct usb_endpoint_descriptor *
535 fsg_ep_desc(struct usb_gadget *g, struct usb_endpoint_descriptor *fs,
536 		struct usb_endpoint_descriptor *hs)
537 {
538 	if (gadget_is_dualspeed(g) && g->speed == USB_SPEED_HIGH)
539 		return hs;
540 	return fs;
541 }
542 
543 /* Static strings, in UTF-8 (for simplicity we use only ASCII characters) */
544 static struct usb_string		fsg_strings[] = {
545 #ifndef FSG_NO_DEVICE_STRINGS
546 	{FSG_STRING_MANUFACTURER,	fsg_string_manufacturer},
547 	{FSG_STRING_PRODUCT,		fsg_string_product},
548 	{FSG_STRING_SERIAL,		fsg_string_serial},
549 	{FSG_STRING_CONFIG,		fsg_string_config},
550 #endif
551 	{FSG_STRING_INTERFACE,		fsg_string_interface},
552 	{}
553 };
554 
555 static struct usb_gadget_strings	fsg_stringtab = {
556 	.language	= 0x0409,		/* en-us */
557 	.strings	= fsg_strings,
558 };
559 
560 /*-------------------------------------------------------------------------*/
561 
562 /*
563  * If the next two routines are called while the gadget is registered,
564  * the caller must own fsg->filesem for writing.
565  */
566 
567 static int fsg_lun_open(struct fsg_lun *curlun, const char *filename)
568 {
569 	int				ro;
570 
571 	/* R/W if we can, R/O if we must */
572 	ro = curlun->initially_ro;
573 
574 	curlun->ro = ro;
575 	curlun->file_length = ums->num_sectors << 9;
576 	curlun->num_sectors = ums->num_sectors;
577 	debug("open backing file: %s\n", filename);
578 
579 	return 0;
580 }
581 
582 static void fsg_lun_close(struct fsg_lun *curlun)
583 {
584 }
585 
586 /*-------------------------------------------------------------------------*/
587 
588 /*
589  * Sync the file data, don't bother with the metadata.
590  * This code was copied from fs/buffer.c:sys_fdatasync().
591  */
592 static int fsg_lun_fsync_sub(struct fsg_lun *curlun)
593 {
594 	return 0;
595 }
596 
597 static void store_cdrom_address(u8 *dest, int msf, u32 addr)
598 {
599 	if (msf) {
600 		/* Convert to Minutes-Seconds-Frames */
601 		addr >>= 2;		/* Convert to 2048-byte frames */
602 		addr += 2*75;		/* Lead-in occupies 2 seconds */
603 		dest[3] = addr % 75;	/* Frames */
604 		addr /= 75;
605 		dest[2] = addr % 60;	/* Seconds */
606 		addr /= 60;
607 		dest[1] = addr;		/* Minutes */
608 		dest[0] = 0;		/* Reserved */
609 	} else {
610 		/* Absolute sector */
611 		put_unaligned_be32(addr, dest);
612 	}
613 }
614 
615 /*-------------------------------------------------------------------------*/
616